An author who conducted 18 months of research on the Oscar Pistorius murder trial agreed with the verdict handed to the South African double-amputee sprinter.

But, the author concluded, only Pistorius knows whether justice was served.

John Carlin, whose book Chase Your Shadow: The Trials of Oscar Pistorius, was released on Monday, told The Guardian what he discovered about Pistorius and the trial during his intensive study.

"Despite having sat through most of the trial and having spent a year and a half researching Pistorius's life, talking to him and to many who knew him well, I do not presume to offer any further clarity on the matter. On my travels for the book-- to Texas, Boston, Reykjavik, London, Milan and all over South Africa - people would ask me the same question again and again: 'Did he mean to do it?'

"I would always reply that I honestly did not know. And now that the trial is over, I am none the wiser - save to say that I think the prosecution overreached itself in pushing for premeditated murder and that I agree with the judge that the evidence did not support the charge."

Perhaps the revelation that Carlin leaves during his first-person story is the fact that he finds Pistorius more sympathetic now than he did when Pistorius initially was charged in the killing of girlfriend Reeva Steenkamp, "when I leapt immediately to the conclusion - as most people did - that he was a murderous monster who had killed his girlfriend in a jealous rage."

"People ask me all the time what I think of Pistorius now that I have probed somewhat into his character and life story," Carlin said. "What I think is that he is a man of extremes: that he is driven and brave, fearful and insecure; that he is courteous and kind, rude and egotistical; that he is crazily romantic, asphyxiatingly possessive; that he is intelligent and self-contained, stupid and hot-headed."

Those facts alone do not confirm innocence or guilt.

"What I do believe now is that both versions submitted before the court - that Pistorius knew it was Steenkamp, that he thought it was an intruder - are equally implausible, even though one of them has to be true," Carlin said.